When an attenuation function, a polarization function, a scattering function, a light shielding function and the like of irradiating lights including a laser beam and natural light are required, there are conventionally used apparatuses operating according to theories varying depending on respective functions. Hence, also articles corresponding to these functions are produced by production steps varying depending on respective functions. For example, for LCD (liquid crystal device), a linear polarizing plate and a circular polarizing plate are used to control optical rotation and birefringence in display. Also in OLED (organic electroluminescence device), a circular polarizing plate is used for prevention of reflection of a light from the outside. Conventionally, iodine is widely used as a dichroic dye in these polarizing plates (polarizing device). An iodine polarizer is prepared by dissolving or adsorbing iodine in or on a polymer material such as polyvinyl alcohol, and stretching its film in the form of a film toward one direction to align a polyiodine complex. When used in a polarizing device, however, the heat resistance and the light resistance of iodine are not sufficient because of a significant sublimation property of iodine.
For this reason, a polarizing device using organic dyes as a dichroic dye has been considered. These organic dyes, however, have a problem that only a polarizing device having fairly poor dichroism is obtained as compared with iodine.
This method also has problems such as troublesome processes of a stretching treatment and the like.
Therefore, other methods have attracted attention recently. For example, there is a wet film-forming method in which a dichroic dye is aligned on a substrate made of glass, a transparent film and the like by utilizing intermolecular interaction of organic dye molecules. As a method of enhancing the dichroic ratio of an aligned dichroic dye, a dichroic dye is aligned in a phase having high orientation order in Patent Document 1. Further, Patent Documents 2 and 3 disclose a polarizing device containing a crystalline structure. However, these polarizing devices have a problem that the devices tends to cause a grain boundary with a domain, thereby causing scattering and depolarization since these polarizing devices have a low symmetry and high order structure. An azo dye having a substituent imparting water-solubility such as a sulfo group, a carboxyl group and the like described in Patent Document 2 is difficult to subject to a uniform alignment treatment by heat aging like in the case of a thermotropic liquid crystal, and it is hard to form a coated film having a smooth surface with the azo dye, generating causes for scattering and depolarization, since the azo dye is a lyotropic liquid crystal.
As alignment treatment methods of a dichroic dye, there are known a vapor deposition method, a rubbing method and an optical alignment method. For example, in Patent Document 4, organic dye molecules are vapor-deposited from a gas phase and aligned on an alignment film. The method described in this document, however, has a problem of a complicated process thereof for production. Patent Document 5 discloses a method of spin-coating and aligning a liquid crystalline azo dye on a rubbed alignment film. Though this rubbing method is widely used conventionally as a method of aligning a liquid crystal compound, it generates static electricity and dust, thus causing a problem with the production process such as necessity of a washing step after the alignment treatment leading to a decrease in yield, and a problem on performance such as lowering of contrast.
On the other hand, an optical alignment method has recently attracted attention as an alignment treatment method instead of this rubbing method, since a washing step after the alignment treatment is not necessary in the optical alignment method. For example, Patent Document 6 discloses a polarizing device obtained by coating and aligning dichroic molecules having a hydrophilic substituent such as a sulfonate group, an amino group, a hydroxyl group and the like on a layer having photoactive molecules (a so-called photo alignment film). Patent Documents 7 and 8 disclose a polarizing device formed by coating and aligning a composition prepared by dissolving a black dichroic dye in an ultraviolet-curable liquid crystal (a so-called guest-host type) on a photo alignment film. The polarizing devices obtained by these methods, however, are all significantly poor in dichroism as compared with an iodine polarizer, and cannot be used in liquid crystal display devices.
Recently, there has been advancement in application development of new polarizing devices aiming at improvement in display performance and the like. Patent Document 9 proposes to suppress depolarization (a so-called depolarization index) of a color filter by providing a polarizing layer (a so-called in-cell polarizing layer) between a color filter layer and a liquid crystal material layer. However, a polarizing layer disposed in a liquid crystal cell is required to attain a desired degree of polarization at a smaller film thickness, and a higher dichroism is necessary for this layer.